Catalyst support

ABSTRACT

A support for a metallic gauze catalyst in a reactor for manufacturing hydrocyanic acid or nitrogen oxides is made up of a plurality of hollow tubular members disposed in a conical configuration. Heat transfer media flows within the hollow tubular members which make up the conical support to maintain a more uniform temperature of the catalyst and permit the use of less costly materials for catalyst support structures.

United States Patent 11 1 1111 3,715,193

Strelzoli 1 Feb. 6, 1973 [5 CATALYST SUPPORT 2,584,080 1 1952 Houpt..23/288J H61 Inventor Samuel SWIM, 12 west 96th 1328322 211322"15211222513113: ....:1./

Street, New York, 10025 2,620,262 12/1952 Hujsak etal ..l65/l75 x 22Filed: March 1,1971

Appl. No.: 119,670

References Cited UNITED STATES PATENTS 6/1967 Law ..165/l69 PrimaryExaminer.loseph Scovronek Attorney-Donald L. Johnson, John F, Sieberthand Shelton B. McAnelly [57] ABSTRACT A support for a metallic gauzecatalyst in a reactor for manufacturing hydrocyanic acid or nitrogenoxides is made up of a plurality of hollow tubular members disposed in aconical configuration. Heat transfer media flows within the hollowtubular members which make up the conical support to maintain a moreuniform temperature of the catalyst and permit the use of less costlymaterials for catalyst support structures.

3 Claims, 2 Drawing Figures PATENIEDFEB .6 ms

SHEET 1 or 2 W i. I

I I I I I I I 1/ FIG. I.

CATALYST SUPPORT BACKGROUND OF THE INVENTION 1. Field of the InventionThe invention relates to the manufacture of hydrocyanic acid andnitrogen oxides from ammonia and air or oxygen by the combustion thereofin the presence of a suitable noble metal catalyst, methane being fedalso for the production of hydrocyanic acid. In particular, theinvention relates to reactor configurations and structures forsupporting the catalyst to achieve long life of catalyst and longuninterrupted operation of the reactor system.

2. Description of the Prior Art Conical shaped catalytic gauzestructures for the manufacture of hydrocyanic acid and oxides ofnitrogen are disclosed in U. S. Pat. Nos. 2,496,999 and 2,552,279 whichdiscuss at length several problems involved in the process. One of theserious problems of the prior art is that of physical failure orbreaking of the catalyst gauze, usually attributed as in U. S. Pat. Nos.3,033,658 and 3,215,495, to embrittlement associated with a depositionof carbon in the cooler regions of the catalyst gauze. Although theconical catalyst structure of the prior art represents a significantimprovement in increasing the production capacity of a given diameter ofreactor, mechanical failure of the catalyst is still experienced at anundesirably high rate in conical gauze systems, apparently largelybecause the benefits of the smaller diameter of the reactor are offsetto some extent by the greater mass of catalyst that is required for agiven diameter in the conical configuration and the greater stressesproduced in the gauze due to the weight and angularity of the catalyst.Thus the present invention includes an aspect related to the provisionof supports for the conical catalyst gauze to minimize stresses due tothe weight that must be supported directly and solely by the gauzeitself.-

Supported catalysts in general are not new inasmuch as they aredescribed in other prior art, such as U. S. Pat. Nos. 2,750,266;3,056,655 and 3,423,185; however, a problem with the structures of thesepatents is that the support systems that have been used are complex andare not conveniently usable in conjunction with a conical shapedcatalyst.

The present invention seeks to provide a thermally regulated support fora conical gauze catalyst system useful in the production of hydrocyanicacid and nitrogen oxides.

In accordance with the present invention a support is provided for aconical shaped metallic gauze catalyst in a reactor used for themanufacture of hydrocyanic acid or oxides of nitrogen by reaction ofammonia and air or oxygen to produce oxides of nitrogen, and ammonia,air or oxygen and a hydrocarbon gas to produce hydrocyanic acid. Thecatalyst support comprises a conical spoked assembly containing aplurality of hollow tubular members connected to a gas distributorsection at the apex of the cone and to a gas collector section at thebase of the cone, and means for supplying a heat transfer fluid to thedistributor and removing it at the collector whereby the catalyst iscooled by the heat transfer fluid by a greater amount in the region ofthe apex than in the region ofthe base of the cone.

The present invention also relates to a gas flowthrough reactorutilizing the aforesaid catalyst support wherein the base to apex axisof the cone is substantially parallel to the flow of gases through thereactor and wherein the base of the cone is nearer the feed point of thegases than the apex of the cone and wherein the gauze catalyst isdisposed on the support on the side thereof which is first contacted bygases flowing through the reactor.

in a typical example of the use of the aforesaid catalyst support,ammonia, air and a hydrocarbon are reacted in the presence of a platinumcontaining gauze catalyst to produce hydrocyanic acid.

With reference now to FIG. 1 of the drawing, the apparatus shown thereinincludes a cylindrical reactor 10 having upper and lower portions 11 and12, respectively. Each reactor section is jacketed for heat controlpurposes, the upper jacket generally being provided with heating throughthe jacket whereas the lower section is generally provided with coolingthrough the jacket. The flow through the reactor 10 is generally in adownward direction indicated in FIG. 1 by the arrow near the referencecharacter 10. The two reactor sections are connected together as byflange 13 providing for convenient assembly and disassembly. The upperreactor section 11 preferably extends downward beyond the flange 13 tominimize undesirable heat losses through the flange and attendant abrupttemperature gradients.

A conically configured catalyst structure is disposed within the reactoras indicated in general by reference character 14. The catalyststructure is a plural layer mesh of platinum, platinum and rhodium alloyand similar mesh materials. As combustible gases flow through thereactor in the direction indicated by the arrow, combustion occurs inthe region of passage of the gases through the catalyst gauze 14 wherebydesired combustion products are produced. In the case where hydrocyanicacid is desired, the principal constituents of the gases fed includeammonia, oxygen or air and a hydrocarbon such as methane. In the casewhere it is desired to produce nitrogen oxides for nitric acid, the feedgases to the reactor are essentially ammonia and oxygen or air. In thecase of HCN the usual temperature of the catalyst gauze is at from aboutl,800 to about 2,400F, preferably 2,0002,200F, typically 2,l00F. [n thecase of nitric oxides the temperature is from about l,650 to about1,700F.

The catalyst gauze is supported by a conical spoke support structureindicated generally by reference character 15 having a lower annulardistributor 16 and upper circular collector 17. The spokes of thesupport are typically six in number equidistantly spaced or distributedaround the cone. Each of the spokes of the support 15 is hollow toprovide for the circulation of a heat control fluid therethrough. Thesupport is cast or fabricated in one or more portions and assembled ifnecessary. Typically, such heat control or heat transfer fluid is steam,water, or molten salt or metal supplied through line 18 connected todistributor l6 and removed through line 19 connected to collector 17.The heat transfer fluid provides for several desirable results. In thefirst place, the cooling desirably maintains the catalyst support at asufficiently low temperature to avoid exceeding melting point, creeppoints or yield points of the materials of construction used. The flowarrangement through the support thus provides for cooling the apexportion of the catalyst structure and for heating the peripheral portionof the catalyst structure near the attachment point thereof to the upperportion 11 of the reactor. It is understood that although the termheating" has been used with respect to the peripheral portion of thecatalyst that in many instances the effect in that region is alsocooling; however, relatively speaking, the cooling effect is morepronounced in the apex region of the catalyst, minimizing cold operationof the periphery of the catalyst which some authorities suggest is atleast partly responsible for breakage of the catalyst in prior artsystems. The angle 21 of the catalyst and support is from about 30 toabout 120, typically 60.

It is readily seen from the foregoing discussion that the support 15 notonly avoids the necessity for the catalyst to support its entirephysical weight but that it also provides for control of the temperatureof the catalyst facilitating operation and warmup of the system onstarting or in brief interruptions of feed during which time heated heattransfer medium is supplied through line 18 to provide heating of thecatalyst to minimize thermal shock to the catalyst.

The materials of construction problem is of considerable importance inthe apparatus of the present invention, a characteristic of the art.Typically, the materials of construction used for the catalyst support15 must be capable of withstanding the temperatures encountered inoperation including momentary upsets and also they must be capable ofresisting corrosion or attack by the materials present in theenvironment. Additionally, the catalyst supports must not be of suchcomposition as would tend to impair the catalytic effect of the catalystdue to poisoning or other action. In some instances a preferred catalystsupport structure is of metal with ceramic coating. Preferably, thematerials of construction for the various portions of the catalystsupport are stainless steels such as SS-304 ELC, 88-3 16, 88-3 17,particularly stainless steels containing 2 to 4 percent molybdenum. Suchmaterials are less costly than other materials required in the prior artsuch as Inconel, HK 40, and Carborundum; however, even these areimproved through the use of the principles of the present invention.

With reference now to FIG. 2 of the drawing, another view of the reactor10 of FIG. 1 is shown in a partially cut-away cross-section.Corresponding reference characters are used to indicate principally thestructure of the catalyst support; viz., the support 15, annulardistributor l6, circular collector 17, the upper extension of the lowerportion 12 of the reactor, and its jacket 20. As indicated in FIG. 2,the catalyst support typified contains six spoke" members; however, itis to be understood that in appropriate instances greater or lessernumbers of spokes such as eight, l0, l2 orfour may be useful ordesirable. As is seen from FIG. 2, the spokes connect to the annulardistributor l6 and also to a conduit portion within the collector 17whereby the heat transfer fluid passing through the spokes is placed incontact with the entire supporting periphery for the catalyst 14 tomaintain heat input thereto by means other than through the catalystitself. As has been discussed, such is desired to minimize the coolingeffect upon the catal st.

EXAMPLE A cylindrical reactor is made as in FIG. 1 having an internaldiameter (10) of 4 feet. The catalyst support is fabricated by weldingfrom 88-304 using six tubes of 2 inches outside diameter with V4 inchwall thickness. The angle 21 is 60.

The catalyst is 90 percent platinum, 10 percent rhodium, 52 mesh, 0.004inch wire screen placed in seven layers, formed from triangular sheetswelded together with a hydrogen torch.

The reactor is fed by a mixture of gas, air and ammonia in proportionsof about 2,500 pounds per hour of ammonia, 63 thousand standard cubicfeed per hour of natural gas and 327 thousand standard cubic feed perhour of air. The feed mixture is preheated to a temperature of 450F. Thecatalyst temperature is 2,000-2,200F. Saturated steam at about psig issupplied through line 18 to the annular distributor 16 of the catalystsupport.

In operation from 50 to 65 percent of the ammonia is converted to HCN,10-15 percent is decomposed and the balanced recovered by reaction withsulfuric acid to produce ammonium sulfate.

lclaim:

l. A support for a conical shaped metallic gauze catalyst in a reactorused for the manufacture of hydrocyanic acid or oxides of nitrogen byreaction of ammonia and air or oxygen to produce oxides of nitrogen andammonia, air or oxygen and a hydrocarbon gas to produce hydrocyanicacid, which comprises, a conical spoked assembly containing a pluralityof hollow tubular members connected to a fluid distributor section atthe apex of the cone and to a fluid collector section at the base of thecone, and means for supplying a heat transfer fluid to the distributorand means for removing it at the collector whereby the catalyst iscooled by the heat transfer fluid by a greater amount in the region ofthe apex than in the region of the base of the cone.

2. A gas flowthrough reactor utilizing the catalyst support of claim 1wherein the base to apex axis of the cone is substantially parallel tothe flow of gases through the reactor and wherein the baseof the cone isnearer the feed point of the gases than the apex of the cone and whereinthe gauze catalyst is disposed on the support on the side thereof whichis first contacted by gases flowing through the reactor.

3. The support in accordance with claim 1 comprising in addition aconical shaped platinum containing gauze catalyst supported by theconical spoked assembly.

i l I i

1. A support for a conical shaped metallic gauze catalyst in a reactorused for the manufacture of hydrocyanic acid or oxides of nitrogen byreaction of ammonia and air or oxygen to produce oxides of nitrogen andammonia, air or oxygen and a hydrocarbon gas to produce hydrocyanicacid, which comprises, a conical spoked assembly containing a pluralityof hollow tubular members connected to a fluid distributor section atthe apex of the cone and to a fluid collector section at the base of thecone, and means for supplying a heat transfer fluid to the distributorand means for removing it at the collector whereby the catalyst iscooled by the heat transfer fluid by a greater amount in the region ofthe apex than in the region of the base of the cone.
 2. A gasflowthrough reactor utilizing the catalyst support of claim 1 whereinthe base to apex axis of the cone is substantially parallel to the flowof gases through the reactor and wherein the base of the cone is nearerthe feed point of the gases than the apex of the cone and wherein thegauze catalyst is disposed on the support on the side thereof which isfirst contacted by gases flowing through the reactor.